1. Field of the Invention
This invention relates to articles capable of being heated by magnetically coupled radio frequency energy.
2. Discussion of the Art
Magnetic susceptors are used to convert energy derived from radio frequency induction heaters to heat energy at a point of application. For example, U.S. Pat. No. 3,461,014 discloses a method for heat sealing and bonding predetermined sealing areas of two units of material, one of which has a heat-fusible plastic surface, comprising the steps of (1) positioning a deposit of fine, discrete susceptor particles selected from the chemical family of ferromagnetic oxides on one of said units at said predetermined sealing areas, (2) bringing said units of materials into opposed, interfacing relation with said deposit interposed therebetween and contiguous to said fusible plastic surface, (3) subjecting said susceptor particles to a magnetic induction field and thereby concentrating heat effect upon substantially only the plastic material immediately contiguous to said particles, and (4) bringing said units into firm contact.
U.S. Pat. No. 3,574,031 discloses a method of heat welding thermoplastic bodies comprising the steps of (1) forming a stratum of susceptor sealant by uniformly dispersing particles of a susceptor material selected from a group consisting of magnetically polar substances and electrically polar substances, excitable by a selected form of indirectly applied energy for raising the temperature of the susceptor material in a thermoplastic carrier compatible with the chemical families of the thermoplastic bodies to be welded, each of said particles having a maximum dimension less than the thickness of the stratum; (2) applying the stratum of susceptor sealant to the bodies in the area to be heat welded; and (3) exposing the susceptor sealant to the selected form of indirectly applied energy to generate heat therein sufficient to soften the carrier and cause the stratum to intimately weld the thermoplastic bodies.
Bonding by induction heating can be used to seal bags and pouches, seal window panes, bind books, and the like.
Induction heating can be used in situations where microwave heating is not suitable, such as, for example, in cases where the materials to be bonded absorb microwave energy, such as polar polymers, wood, or materials containing non-magnetic conductive particles. In these situations, it may be desirable to heat the bond area only and not the material to be bonded.